NMT223 - Image Digitization & Display (Chapter 6)
If the patient has a heart rate of 80 bpm and the gate is set for 24 frames/cycle, how many milliseconds are in each frame?
(60 sec/min)/(80 beat/min) = 0.75 sec/beat (0.75 sec/beat)/(24 frames/beat) = 0.031 sec/frame = 31 ms/frame
How can image noise be reduced?
-Increase counts or imaging time -Change matrix size -Apply filtering methods
How many pixels are in a 128x matrix?
128 x 128 = 16384
When is 128x best?
128x is best when good resolution is needed but counts are not high
When is 256x best?
256x is best when good spatial resolution is needed and plenty of counts are available
What is the resulting pixel size if X2 PreZoom is applied to 6mm unzoom pixels?
3mm pixels
If the FOV is 600mm wide on a 128x matrix, what is the pixel size?
600mm/128 = 4.7mm
When is 64x best?
64x is best when counts are low and excellent spatial resolution is not needed
What is an LUT?
A Look-up table is a table listing counts/pixel values and their corresponding gray or color levels (LUT assigns a specific shade of gray to a specfic count/pixel value; tjhe blackest shade is assigned to the highest cts/pixel value and the lightest shade to zero cts/pixel value)
What is an image matrix?
A matrix is a grid-like arrangement in which events are placed (64x64, 128x128, 256x256, etc.)
What is a pixel?
A pixel refers to an individual position on a grid
What is a screen capture?
A screen capture saves the screen as a digital image including annotation, formatting, computer analysis results, etc. This saves the images as they have been manipulated/processed
What is an ADC?
Analog to Digital Converter
What is gray scale?
Basic image display; each pixel is assigned a gray scale number based on the number of counts
What is byte mode?
Byte mode allows each pixel to accumulate up to 255 counts
How is byte mode denoted?
Byte mode is denoted by x8 after the matrix
What are color scales?
Color scales assign a color to each count/pixel value using a three-color LUT
What is contrast?
Contrast is the change in image intensity per incremental change in count/pixel values (Example: In a high contrast image, there would be a greater difference in displayed intensity between 150 count and 200 count pixels than there would be in a low contrast image)
What is digital zoom?
Digital zoom multiplies X and Y values by a digital zoom value before or after putting them into the image matrix
How many image buffers do dynamic images require?
Dynamic images require two buffers - one to acquire and one to store the acquired dynamic frame
What is gated frame mode?
Gated frame mode uses the patient's ECG signal to create a composite dynamic movie of the beating heart; it is acquired over many heart beats
How many image buffers go gated studies require?
Gated studies require X buffers, where X is the number of frames per cycle
If a X2 post-acquisition zoom is applied to a 64x64 matrix, which pixels will occupy the full display screen?
If a X2 post-acquisition zoom is applied to a 64x64 matrix, the middle 32x32 pixels will occupy the full display screen
What is image noise?
Image noise refers to counts that appear on an image as a result of random fluctuations
What are analog images?
In analog images, the location of each event is different from the location of all other events (No two X/Y coordinates are the same)
What is digital imaging?
In digital images, the X and Y values corresponding to each event are limited to certain discrete values (imagine plotting each location as a square on a grid)
What is frame mode?
In frame mode an image matrix is created and each count is assigned to a pixel in that matrix
What is list mode?
List mode sequentially stores each count separately as an X,Y value rather than placing it on a matrix
How does pixel overflow appear on a scan?
Pixel overflow can appear as an area of overly saturated pixels that lack detail
How is pixel size determined?
Pixel size = (FOV in mm)/(Matrix Dimension)
If the FOV remains the same and the matrix increases, how does pixel size change?
Pixel size is decreased
If the FOV increases and the matrix remains the same, how does pixel size change?
Pixel size is increased
What should pixel size generally be?
Pixel size should be between 1/3rd to 1/2 of the system resolution
What is the name for digital zoom that is applied AFTER assigning values to the image matrix?
Post-Acquisition Zoom (Magnification)
What is the name for digital zoom that is applied BEFORE assigning values to the image matrix?
Pre-Acquisition Zoom
What is the max improvement of resolution that can be achieved using PreZoom?
PreZoom can improve resolution up to the spatial resolution of the gamma camera
What is the disadvantage of smoothing?
Smoothing can result in a slight decrease in reslution and detail with blurring
What is smoothing?
Smoothing is used to make a noisy image look less noisy by bringing the extreme outlier pixels (very high or very low) back closer to the local average
How many image buffers do static images require?
Static images require one image buffer
How is the LUT applied differently for static vs dynamic acquisitions?
Static: Blackest shade = Max cts/pixel Lightest shade = Zero cts/pixel Dynamic: Blackest shade = Max cts/pixel in ENTIRE set of images Lightest shade = Zero cts/pixel
What is the most common type of smoothing?
The most common type of smoothing is a 9-point smoothing
What is the third dimension of each grid?
The third dimension of each grid is the number of counts in the pixel
What is the disadvantage of too much post-acquisition zoom?
Too much post-acquisition zoom decreases resolution
List the image display devices used in nuclear medicine
Video display terminal Liquid Crystal Display (LCD) monitor Multi-formatter Hard Copies (Printers, film) PACS (Picture Archiving/Communications Systems) DICOM (Digital Imaging and Communications in Medicine)
What is word mode?
Word mode allots two bytes to each pixel address, allowing up to 65535 counts to be accumulated in each pixel
How is word mode denoted?
Word mode is denoted by x16 after the matrix
Which mode is preferred for nuclear medicine studies?
Word mode is preferred for all nuclear medicine studies
